The present invention relates to the art of portable emergency breathing apparatus and, more particularly, to improvements in connection with such apparatus in which breathing gas from a source in continuously supplied at a controlled rate to the user.
Portable emergency breathing apparatus in which breathing gas from a source such as a compressed oxygen container is continuously supplied at a controlled rate to a face mask or hood worn by the user is generally referred to as open circuit apparatus in that the gas breathed by the user from the container is exhaled to atmosphere. Such apparatus generally includes a pressure reducing valve assembly and an adjustable flow restriction cooperable therewith to control the rate of flow of breathing gas to the user, and a pressure gauge for indicating the pressure in the breathing gas container and thus the availability of breathing gas with respect to the duration of use of the apparatus.
There are a number of potential uses for short duration apparatus of the foregoing character which would, for example, provide a five minute or ten minute breathing gas supply. Often, the environments of such potential use are such that storage of a large number of units is required in a relatively small storage space. Among the disadvantages with respect to such units heretofore available is the fact that the pressure reducing valve and pressure gauge are generally individually coupled with the supply container through the use of standard pipe couplings and fittings, whereby the apparatus is rather bulky and has exposed parts which are subject to easy damage either in connection with the storage thereof, the retrieval from storage, or in use. More particularly in this respect, the exposed parts are subject to contact with objects including other breathing apparatus in a common storage area, the surface on which the apparatus is stored, and numerous objects which can be encountered during use. Moreover, the bulkiness of the apparatus increases the required space for storage thereof, and this is especially disadvantageous in connection with the storage of a large number of units where storage space is of a premium, such as in an airplane. Still further, the use of structurally separate valves and pressure gauge components and pipe couplings and fittings in connection with the mounting thereof on a supply container renders the apparatus undesirably heavy.
Another disadvantage, not necessarily limited to short duration apparatus, resides in the inability to maintain a substantially constant flow rate throughout the designed duration of the unit. More particularly in this respect, the pressure regulator of the unit is intended to respond to the pressure drop thereacross between the supply cylinder and the user so as to maintain a substantially uniform rate of gas flow to the user throughout the designed duration of the unit and regardless of the cylinder pressure which continuously decreases during use of the apparatus. Pressure regulator arrangements heretofore provided for use in emergency breathing apparatus have not functioned satisfactorily in this respect and, in addition to not provide a desired uniformity in flow rate during use of the apparatus, often function such that the flow rate falls below the desired flow rate prior to use of the apparatus for the designed duration thereof. Moreover, as the designed time duration is approached, descent of the flow rate progressively increases, whereby the flow rate not only falls below the desired flow rate but does so to such an extent and with such rapidity that usefulness of the apparatus is terminated prior to reaching the designed time duration. It will be appreciated that the latter is potentially hazardous to a user of the apparatus who, for example, remains in a dangerous environment based on an erroneous assumption that the apparatus will be effectively operable for the designated period of time. Efforts to avoid this problem have included the use of larger supply gas cylinders which is undesirable in that this increases the size and weight of the apparatus. Moreover, this approach does not resolve the primary problem, namely the inability of the pressure regulator to function to achieve a uniform flow rate throughout the designed duration.